The principles of induction sealing packages or other containers are well known. See, for instance, U.S. Pat. Nos. 3,864,186 and 3,730,804. As an example, induction sealing is commonly used to seal caps onto polyethylene bottles, such as are used in the food and pharmaceutical industries. Such capseals might have an upper layer of paper, an intermediate aluminum foil layer and an inner layer of a thermoplastic polyolefin, such as polypropylene, polyethylene, etc. The capseal is placed onto the bottle with the polymer layer in facial contact, and covering, the lip of the bottle. The bottle lip is formed of a compatible polymer to the capseal polymer layer.
An electric generator is used with a coil to produce a high-frequency electromagnetic field adjacent the coil. The bottlemouth with capseal thereon is passed through this field, with heat-producing eddy currents thereby being induced in the foil layer of the capseal. This heat is conducted to the polymer layers in a sufficient degree to cause the respective thermoplastic materials to fuse, sealing the bottle.
As will be seen in the disclosure that follows, the present invention came about in an endeavor to make an inductively-sealed package for a stack of chewing gum sticks. These chewing gum packages are formed by a planar wrapper which is folded about the rectangular-shaped stack. The mid-line of the package (where the "ends" of the wrapper meet) is first formed by sealing overlapping wrapper portions along the length of the stack. The two opposite sides of the package thereby left open are then closed by folding the wrapper upon itself and sealing the folded portions. This wrapping technique is, in substance, the typically same employed by anyone who has ever wrapped a gift package.
Considerations in inductive sealing of such a chewing gum package included making a wrapper that could be inductively sealed to itself, met regulations governing packaging of such foodstuffs, and which could be readily produced in massive quantities. The induction sealing apparatus itself also needed to be capable of conveying a pre-folded wrapped gum package, compressing the folded sides of the package into facial engagement, and generating heat-producing eddy currents in the wrapper sufficient to cause induction sealing but not adversely affecting the chewing gum. In this latter regard, it will be borne in mind that each stick of gum also has a wrapper including a foil layer susceptible to inductive heating. A very localized electromagnetic field was therefore required to prevent undesired heating of the gum sticks, but still seal the package sides.